The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Variable displacement engines provide improved fuel economy and torque on demand using cylinder deactivation. When high output torque is required, all cylinders of a variable displacement engine are supplied with fuel and air. At low engine speeds, low load, and/or other inefficient conditions, some of the cylinders (for example only, half of the cylinders) may be deactivated to reduce throttle losses and improve fuel economy. Throttling losses, also known as pumping losses, are associated with work that an engine performs to pump air from the relatively low pressure of an intake manifold, across intake and exhaust valves, and out to the atmosphere. The deactivated cylinders prevent airflow across their respective intake and exhaust valves, thereby reducing pumping losses.
Valve lifters are used to open and close the intake and exhaust valves. When cylinder deactivation is desired, a solenoid that communicates with the valve lifters may be activated to allow pressurized oil to flow to ports in the valve lifters. The pressurized oil unlatches locking pins in the ports, thereby making the valve lifters collapsible. As such, rotational movement of cam lobes on the camshafts cannot be translated into translational movement of the intake and exhaust valves via the valve lifters. When the cylinder is deactivated, the intake and exhaust valves associated with the cylinder are closed.